Secondary Emission Mass Spectrometer (SEMS) will be built by Gatan, Inc. and Extranuclear Labs and owned by BEIB Rental Program. It is anticipated that this facility will contribute to research programs in a number of Institutes, specifically NIMH (S. Markey) and NHLBI (H. Fales). The SEMS will have the following features: (1) Ultra-high Vacuum System; (2) Rapid linear motion multi-specimen holder permitting normal and transmission SIMS modes of operation; and (3) Energy analyzed ion gun (.05 - 10 kV) with deflector, pulser, and rastering. The ion gun will allow us to bombard the specimen with ions free of neutrals or by energetic neutrals only.